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What is a force? A force is a push or pull from one object to another object Examples: Earth’s gravitational pull on us, you pushing a chair, a table supporting a book
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What is a force? All forces have both size and direction The unit of force is the Newton (N) What other concepts have both a size and direction?
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Net Forces The net force is the combination all of the forces acting on the object Whenever more than one force act on an object, always sum the forces into a single net force
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Forces in the Same Direction When forces act in the same direction, you add the forces together The net force will be in the same direction as the two original forces F1= 5 N Fnet= 8 N F2= 3 N
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Forces in the Opposite Direction When two forces act in opposite directions, you subtract the smaller force from the larger force The net force will be in the direction of the larger forceF1= 2 N F2= 7 N Fnet= 5 N
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Balanced Forces When the sum of the forces acting on an object equals zero, the forces are said to be balanced. Balanced forces are equal in size and opposite in direction
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Balanced Forces- Newton’s 1stLaw There is no change in motion when the forces are balanced. A stationary object remains stationary A moving object has constant velocity
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Unbalanced Forces When the sum of the forces are non- zero, there are unbalanced forces acting on the object Unbalanced forces produce a change in motion, so they are necessary to cause accelerated motion
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The Big Idea Unbalanced forces result in a net force The net force causes the object to accelerate This acceleration can be predicted and described
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Force, Mass, andAcceleration An object accelerates when a net force acts upon it The net force is equal to the mass times the acceleration: F = ma This relationship is Newton’s 2nd Law
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Force, Mass, and Acceleration The acceleration of the object depends on both the forces acting on the object and the mass of the object The net force and acceleration are always in the same direction!!F1= 2 N F2= 7 N Fnet= 5 N a
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Example 1 How much force is needed to accelerate a 30 kg scooter at a rate of 1 m/s2? F = ma F = (30 kg) x (1m/s2) F = 30 N
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Example 2 How much force is needed to accelerate a 0.5 kg baseball at a rate of 0.04 m/s2? F = ma F = (0.5 kg) x (0.04 m/s2) F = 0.2 N
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